A) Sandton Brussels Centre because it is the only one near a railway station (Gare centrale, 2 min walk)
B) No idea - I live here so don't stay in Brussels hotels.
Sweet Brussels B&B are liars, btw - I had to look up their location and on their website, under "Access" they claim to be 5 mins WALKING DISTANCE from Gare du Midi AND from the Grand' Place, and this is a physical impossibility! Under "neighbourhood" they appear to be trying to claim to be close to the Sablon. In fact, they are in a not very nice area about 15 mins walk (allowing for crossing various roads and big junction; 10 if there were no obstacles) from Gare du Midi. If you stay there, then coming from Gare du Midi, on the left-hand side of the railway lines (Esplanade de l'Europe), don't walk on the side of the road next to the tracks, unless you like the smell of urine... It would actually be more pleasant to take the metro 1 stop to Lemonnier.